interface A {
    double f(double x,double y);
}
class B implements A{
   public double f(double x,double y) {
	return x*y;
    }
   int g(int a,int b) {
	return a+b;
   }
}
public class E{
    public static void main(String args[]){
	A a=new B();
	System.out.println(a.f(3,5));
	B b=(B)a;
	System.out.println(b.g(3,5));
    }
}
